Positive Electrode Active Material, Positive Electrode, All-Solid-State Battery, and Method of Producing Positive Electrode Active Material

Abstract

A positive electrode active material comprises an active material particle and a coating film. The coating film covers at least part of a surface of the active material particle. The coating film includes a first compound or a second compound. The first compound includes a glass network forming element. The first compound does not include phosphorus. The first compound satisfies the relationship of “0.55≤C Li /C E ≤1.03”. The second compound includes phosphorus and the glass network forming element. The second compound satisfies the relationship of “0.20≤C P /C E ≤8.72”. Each of C Li , C E , and C P represents an element concentration measured by XPS. C Li represents an element concentration of lithium. C E represents an element concentration of the glass network forming element. C P represents an element concentration of phosphorus.

What is claimed is: 
     
         1 . A positive electrode active material comprising:
 an active material particle; and   a coating film, wherein   the coating film covers at least part of a surface of the active material particle,   the coating film includes a first compound or a second compound,   the first compound includes a glass network forming element,   the first compound does not include phosphorus,   the first compound satisfies a relationship of an expression (1):   
       
         
           
             
               
                 
                   
                     0.55 
                     ≤ 
                     
                       
                         C 
                         Li 
                       
                       / 
                       
                         C 
                         E 
                       
                     
                     ≤ 
                     
                       
                         1 
                         . 
                         0 
                       
                       ⁢ 
                       3 
                     
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
         the second compound includes phosphorus and the glass network forming element, 
         the second compound satisfies a relationship of an expression (2): 
       
       
         
           
             
               
                 
                   
                     0.2 
                     ≤ 
                     
                       
                         C 
                         P 
                       
                       / 
                       
                         C 
                         E 
                       
                     
                     ≤ 
                     
                       
                         8 
                         . 
                         7 
                       
                       ⁢ 
                       2 
                     
                   
                 
                 
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
         in the above expression (1) and the above expression (2), 
         each of C Li , C E , and C P  represents an element concentration measured by X-ray photoelectron spectroscopy, 
         C Li  represents an element concentration of lithium, 
         C E  represents an element concentration of the glass network forming element, and 
         C P  represents an element concentration of phosphorus. 
       
     
     
         2 . The positive electrode active material according to  claim 1 , wherein the glass network forming element is boron. 
     
     
         3 . The positive electrode active material according to  claim 1 , wherein the second compound further satisfies a relationship of an expression (3): 
       
         
           
             
               
                 
                   
                     0.49 
                     ≤ 
                     
                       
                         C 
                         Li 
                       
                       / 
                       
                         ( 
                         
                           
                             C 
                             P 
                           
                           + 
                           
                             C 
                             E 
                           
                         
                         ) 
                       
                     
                     ≤ 
                     
                       2 
                       ⁢ 
                       
                         .38 
                         . 
                       
                     
                   
                 
                 
                   
                     ( 
                     3 
                     ) 
                   
                 
               
             
           
         
       
     
     
         4 . The positive electrode active material according to  claim 1 , wherein the positive electrode active material has a covering rate of 89% or more, and the covering rate is measured by X-ray photoelectron spectroscopy. 
     
     
         5 . A positive electrode comprising the positive electrode active material according to  claim 1  and a sulfide solid electrolyte. 
     
     
         6 . An all-solid-state battery comprising the positive electrode according to  claim 5 . 
     
     
         7 . A method of producing a positive electrode active material, the method comprising:
 (a) preparing a mixture by mixing a coating liquid and an active material particle; and   (b) producing a positive electrode active material by drying the mixture, wherein   the coating liquid includes a first solute or a second solute and a solvent,   the first solute includes a glass network forming element,   the first solute does not include phosphorus,   the first solute satisfies a relationship of an expression (4):   
       
         
           
             
               
                 
                   
                     0 
                     ≤ 
                     
                       
                         n 
                         Li 
                       
                       / 
                       
                         n 
                         E 
                       
                     
                     ≤ 
                     1 
                   
                 
                 
                   
                     ( 
                     4 
                     ) 
                   
                 
               
             
           
         
         the second solute includes phosphorus and the glass network forming element, 
         the second solute satisfies a relationship of an expression (5): 
       
       
         
           
             
               
                 
                   
                     0.11 
                     ≤ 
                     
                       
                         n 
                         P 
                       
                       / 
                       
                         n 
                         E 
                       
                     
                     ≤ 
                     9 
                   
                 
                 
                   
                     ( 
                     5 
                     ) 
                   
                 
               
             
           
         
         in the above expression (4) and the above expression (5), 
         n Li  represents a molarity of lithium in the coating liquid, 
         n E  represents a molarity of the glass network forming element in the coating liquid, and 
         n P  represents a molarity of phosphorus in the coating liquid. 
       
     
     
         8 . The method of producing a positive electrode active material according to  claim 7 , wherein the glass network forming element is boron. 
     
     
         9 . The method of producing a positive electrode active material according to  claim 7 , wherein the second solute further satisfies a relationship of an expression (6): 
       
         
           
             
               
                 
                   
                     0 
                     ≤ 
                     
                       
                         n 
                         Li 
                       
                       / 
                       
                         ( 
                         
                           
                             n 
                             P 
                           
                           + 
                           
                             n 
                             E 
                           
                         
                         ) 
                       
                     
                     ≤ 
                     
                       1 
                       ⁢ 
                       
                         .05 
                         . 
                       
                     
                   
                 
                 
                   
                     ( 
                     6 
                     ) 
                   
                 
               
             
           
         
       
     
     
         10 . The method of producing a positive electrode active material according to  claim 7 , wherein the solvent includes water. 
     
     
         11 . The method of producing a positive electrode active material according to  claim 7 , wherein the (b) includes drying the mixture by spray drying.